> $(LIBPC) is a single directory name, so I suggest dropping the “for” loop.

Ok, here is a version without loop. I also added "-" before the if to mimick other lines of the bininstall target.

Does it look better now?

> (...) there is technically still a race with “libainstall” and “bininstall” both testing and creating the same directory.

Sorry, I don't understand. Is it an issue in practice to create the same directory twice "at the same time"? Are you able to reproduce the bug?

Please try my use case: "./configure && make && make -j10 install" and enjoy the partial installation :-) (The python binary is installed in bin/ but it doesn't work because the stdlib is completly missing.)